Contrails

The white condensation trails left behind jet aircraft are
called contrails (condensation trails).

Contrails form when hot, humid
air from jet exhaust mixes with environmental air of low vapor
pressure and low temperature. The mixing is a result of
turbulence generated by the engine exhaust.
Cloud formation by a mixing process is similar to the
cloud you see when you exhale in cold air and “see your
breath.” (More on contrails, including an animation from the shuttle)

The figure represents how saturation
vapor pressure varies as a function of temperature.
The white lines are the saturation vapor pressure for ice and water as a
function of temperature (Chapter 4). The applet demonstrate how mixing two air parcels, both parcels are can result in a saturation and the formation of a
cloud (instructions). The temperature of the jet engine exhaust is off to the right of the figure, you control the environment the jet is flying through by moving the red dot.

What environmental conditions are favorable for the formation of contrails?

Adjust the environment by dragging the mouse pointer (hold mouse
button while moving) to set the temperature and humidity of the
environment. Click on Fly button to start the plane moving. You
can change the atmospheric conditions while the plane is flying.

You have control over three aspects of this simulation:

The degree of supersaturation (the amount of the red line
that falls to the right of the saturation vapor pressure curve)
impacts the density of the contrail.

The relative humidity impacts the rate of dissipation of the
contrail

The wind speed (there is a maximum wind, like a jet core,
around -45C) impacts the rate of spreading of the contrail.